The subject matter of the present invention is radiation-setting polyesters which have functional (meth)acrylate groups, are branched in the main chain and/or have aliphatic side chains, and in which no more than 90% of the hydroxyl groups have been replaced by radiation-setting functional groups.
(Meth)acrylate-functional polyesters and polyester urethanes are known. They serve primarily as raw materials for lacquers which are crosslinked with reactive diluents and photoinitiators to form hard films. Without reactive monomers they are mostly fabricated from solutions. By the addition of tackifying resins it is possible to produce tacky-surfaced coatings with such (meth)acrylated oligomers or polymers.
The processes for making macromeric polymers from polymers, i.e., for making polymers which can be set by radiation by means of their functional groups, are various. For example, ways are described in DE-OS No. 28 38 691 and DE-OS No. 30 00 308, through the esterification of hydroxyl polyesters with acrylic acid. The problem with this process is that these esterification reactions do not take place completely, and therefore unreacted monomers are either removed by complicated distillation methods or they have to be bound by reaction with epoxides, for example. A way that combines both methods is described in EP-PS No. 0 054 105.
Another method is the reaction of hydroxyl polyesters with acid anhydrides and then with glycidyl esters of (meth)acrylate-functional monomers according to U.S. Pat. No. 4,158,618, in which an internal photoinitiator is installed in the polymer by the use of halogenated, cyclic anhydrides.
Often the introduction of (meth) acrylate groups into polyesters is accomplished through diisocyanates; either isocyanato prepolymer is produced, which is then reacted with a hydroxyl (meth)acrylate, or the polyester is reacted with an adduct of diisocyanate and hydroxyalkyl (meth)acrylate (U.S. Pat. 4,174,307 and U.S. Pat. 4,164,486).
In U.S. Pat. 4,174,307, monomers or oligomers containing (meth)acrylate groups and having very low molecular weights are used. The (meth)acrylated polyesters according to U.S. Pat. 4,164,486 are polyesters which contain dimeric fatty acid and ethoxylated bisphenol A to improve their adhesion to metals. On the basis of their composition, these products are solid at room temperature and, at higher molecular weights, they have such great viscosities that they can be fabricated only from solution and/or with the addition of monomeric reactive diluents. The preparation of acrylate-functional polyethers by reaction with isocyanatoalkyl(meth)acrylate is described in U.S. Pat. 4,233,425.
The known (meth)acrylate-group-containing polyesters which are accessible through diisocyanates have it in common that they are either built up mostly linearly by the functional polyester components, or, if the main chain is branched, they are formed from polyesters of low degrees of condensation. If high viscosities occur after the functionalization, especially in the case of branched base polyesters of high molecular weight, the products are fabricated from solutions and/or with large additions of monomeric reactive diluents. To obtain hard, scratch-resistant coating films after the crosslinking, additional unsaturated monomers are installed and/or the hydroxyl groups are substituted as completely as possible with polymerizable acrylic groups, in spite of the difficulties described above.
The problem therefore existed of developing (meth)acrylate-group-containing macromers on the basis of polyesters which are still liquid at room temperature despite relatively high molecular weight, and can therefore be processed without solvents. At the same time, even in the case of the incomplete replacement of the hydroxyl groups of the polyester with isocyanates containing unsaturated groups, it is to be possible to achieve a sufficient cohesive build-up of the polyesters by electron radiation without monomeric reactive diluents and photoinitiators.